An ultraviolet absorbent has been used together with various resins, for providing the resins with ultraviolet absorptivity. Inorganic or organic ultraviolet absorbents are used as the ultraviolet absorbents. Inorganic ultraviolet absorbents (see, for example, JP-A-5-339033 (“JP-A” means unexamined published Japanese patent application), JP-A-5-345639, and JP-A-6-56466 and others) are superior in durability such as weather resistance and heat resistance, but the degree of freedom in selecting the compound is limited, because the absorption wavelength is determined by the band gap of the compound, and in addition, there is no inorganic absorbent capable to absorb the light in a long-wavelength ultraviolet (UV-A) range of around 400 nm, and even if there is an absorbent capable to absorb the light in the long-wavelength ultraviolet light, the absorbent develops color, because it has an absorption also in the visible range.
In contrast, the degree of freedom in designing structures is much higher for organic ultraviolet absorbents, and thus, it is possible to obtain an absorbent having a various absorption wavelength by designing the absorbent structure properly.
Various organic ultraviolet absorbent systems have been studied, and two ways of thinking, namely, use of an absorbent having the maximum absorption wavelength in the long-wavelength ultraviolet range and use of a high concentration of absorbent are considered for absorbing the light in the long-wavelength ultraviolet range. However, the absorbents disclosed in JP-A-6-145387 and JP-A-2003-177235 and others having the maximum absorption wavelength in the long-wavelength ultraviolet range were lower in light stability, and their absorption capacity declines over time.
In contrast, benzophenone- and benzotriazole-based ultraviolet absorbents are relatively higher in light stability, and increase in concentration or film thickness leads to relatively clear blocking of the light in the longer-wavelength range (see, for example, JP-A-7-2005-517787 and JP-A-7-285927 and others). Further, benzoxazinone-based ultraviolet absorbents are also known (see, for example, JP-A-62-11744). However, when such an ultraviolet absorbent is coated as it is mixed with a resin and others, the film thickness is normally at most about dozens of μm. In order to block the light in the longer-wavelength range by this film thickness, it is necessary to add the ultraviolet absorbent in a significantly higher concentration. However, a mere increase in concentration only resulted in a problem of precipitation and bleed out of the ultraviolet absorbent during long-term use. There are some ultraviolet absorbents that are irritative to skin and accumulate in the body among the benzophenone- and benzotriazole-based ultraviolet absorbents, and thus, intensive care should have been given to these compounds during use.